Manufacture of Temperature Calibrators

1. TEMPERATURE CALIBRATORS Temperature plays a key role in many industrial and commercial processes. Examples include monitoring cooking temperature in food processing, measuring the temperature of molten steel in a mill, verifying the temperature in a cold storage warehouse or refrigeration system, or regulating temperatures in the drying rooms of a paper manufacturer. A temperature transmitter will use a measuring device to sense the temperature, and then regulate a 4-20 mA feedback loop to a control element that affects the temperature (Fig. 1). The control element might consist of a valve that opens or closes to allow more steam into a heating process or more fuel to a burner. The two most common types of temperature sensing devices are the thermocouple (TC) and resistive temperature detector (RTD). You can source a temperature, provide loop power, and measure the resulting output current. Process temperatures can be verified using a temperature calibrator or digital thermometer. The performance of a thermostat or temperature controller can be determined by measuring the outputs while applying a temperature signal to the input. The performance of a temperature indicator can be verified by applying a calibrated signal to the sensor input and noting the results. HART “smart” transmitters require digital adjustment if found to be out of specification. This task requires a precision calibrator and a digital configuration tool. Dry Well Calibrator: A temperature calibrator that uses a precision oven to source precise temperature. This style of calibrator is often used for the verification of temperature sensors. Excitation current: A constant current applied to an RTD probe to determine actual resistance for temperature measurement. Typical values are 2 mA or less to minimize self-heating of the probe. IPTS-68: International Practical Temperature Scale of 1968. A temperature standard adopted in 1968 that uses intrinsic standards to define the measurement of temperature. Address: 27th KM Stone, Bangalore National Highway NH4, Chembarambakkam, Chennai, Tamil Nadu 600123.

2. ITS-90: International Temperature Scale of 1990. A temperature standard adopted in 1990 that uses intrinsic standards to define the measurement of temperature. This standard modifies the intrinsic standards of IPTS-68 with additional intrinsic references. Lead Resistance Compensation: A compensation method used with 3 and 4 wire RTDs and resistance measurement. This method negates the error associated with lead resistance when making an RTD measurement. Address: 27th KM Stone, Bangalore National Highway NH4, Chembarambakkam, Chennai, Tamil Nadu 600123.

3. Reference Temperature: The temperature at which a thermocouple temperature measurement is referenced. For Fluke Calibration tools, this is the temperature where the thermocouple mini-plug is connected to the calibrator. R∅ ∅: The resistance value of an RTD probe at 0°C. Example PT100-385, R∅ = 100Ω. RTD: Resistance Temperature Device, a temperature measurement sensor that has predictable changes in resistance with a change in temperature. The most common RTD is the platinum PT100-385. Seebeck Effect: Thermoelectric effect in which the voltage potential increases with temperature (thermocouples) in a junction of dissimilar metals. Triple point of water: This temperature reference point is the intrinsic standard at which water is liquid, ice and gas. This reference point defines 0.01°C. Address: 27th KM Stone, Bangalore National Highway NH4, Chembarambakkam, Chennai, Tamil Nadu 600123.